1. Field of the Invention
The present invention relates to a construction machine having an improved structure for protecting a cab and ensuring an intra-cab operator space in the event of a roll over of the construction machine.
2. Description of the Related Art
In a hydraulic excavator, as shown in FIG. 7, an upper rotating body 2 is mounted on a lower traveling body 1 of a crawler type so as to be rotatable about an axis O which is vertical to the ground, and a cab 4 as an operating room for an operator to get thereon is installed on either the right or the left side (the left side in the following description) of an upper frame 3 of the upper rotating body 2. Further, a working attachment 6 including a boom 5 is mounted to be raised and lowered to the right of the cab 4.
In FIG. 7, the numeral 7 denotes a counter weight provided at a rear end portion of the upper frame 3.
As shown in FIG. 8, the upper frame 3 is provided at a left front portion thereof with a cab mounting section 8, and the cab 4 is mounted on the cab mounting section 8 through anti-vibration mounts 9 for shock absorption which are disposed at four corners of the bottom of the cab.
As disclosed in Japanese Patent Laid-Open Publication No. 2004-189089 (Patent Document 1) and Patent No. 3671790 (Patent Document 2), the anti-vibration mounts 9 each includes an elastic member such as anti-vibration rubber to support the cab 4 elastically and movably in the vertical and horizontal directions with a constant vertical stroke. Therefore, the vibration of the cab 4 is cushioned with the anti-vibration mounts 9.
In connection with the hydraulic excavator, it is prescribed as a cab standard (ROPS) that, in the event of a roll over (tip over) of the construction machine, deformation of the cab 4 should be capable of being suppressed so as to ensure an operator space called DLV (Deflection-Limiting Volume) within the cab.
As a structure for meeting the ROPS standard, there is known a structure (Japanese Patent Laid-Open Publication No. 2005-35316, hereinafter referred to as Patent Document 3) wherein a guard member for reinforcing the cab 4 is mounted at an important portion (e.g., an upper half) of the cab 4 or a structure (Japanese Patent Laid-Open Publication No. 2000-229548, hereinafter referred to as Patent Document 4) wherein a guard member is attached to the upper frame 3 so as to cover the cab.
However, in the structure of Patent Document 3 wherein the guard member is attached to the cab 4 alone, the cab 4 becomes powerless against an external force acting in a direction to strip off the cab from the upper frame 3 in the event of a roll over of the machine, with consequent likelihood of the cab 4 being disengaged from the upper frame 3, although there is obtained a reinforcing effect for the cab 4 itself.
On the other hand, in the structure of Patent Document 4 wherein the guard member is attached to the upper frame, this structure is effective in point of preventing disengagement of the cab 4, but in a construction machine provided with the anti-vibration mounts 9, as shown in FIG. 8, there arises drawback that the shock absorbing function of the mounts 9 is killed by the guard member.